Rolling slide member, rolling bearing using same, and method for manufacturing rolling slide member

ABSTRACT

A rolling-sliding member that is high in hardness and continues to have a passivation film reliably even after being subjected to a process that does not require any processing for removal of scale, etc., as well as a rolling bearing using the same and a method for manufacturing the rolling-sliding member.

RELATED APPLICATIONS

The present application is a divisional application of U.S. applicationSer. No. 15/999,613 filed Aug. 20, 2018, which in turn is a U.S.national stage application of PCT/JP2017/005394 filed Feb. 15, 2017.Each of these prior applications is incorporated herein by reference inits entirety.

TECHNICAL FIELD

The present invention relates to a rolling-sliding member, a rollingbearing using the same, and a method for manufacturing a rolling-slidingmember.

BACKGROUND ART

Rolling bearings are used broadly in various fields. For example, invehicle slide doors, rolling bearings (roller bearings) are used so thata slide door can be opened and closed smoothly along a slide rail thatis provided on each side of a vehicle body. Rolling bearings are alsoused in slide doors of industrial machines, warehouses, etc. Rollingbearings for a slide door need to be high in strength so as to be ableto support the weight of the slide door and not to be damaged ordeformed by, for example, an impact load occurring when the door isopened or closed. Conventionally, rolling bearings of this type employSUS440C which is of a martensite type and belongs to a class that ishighest in hardness among stainless steels.

Incidentally, slide rails of a slide door may be installed in such astate as to be exposed directly to an external environment (ambientatmosphere). In this case, rolling bearings are also required to be highin corrosion resistance because they are put in such an exposed-to-waterenvironment as to be easily exposed to a cleaning liquid for vehiclewashing, an aqueous solution of calcium chloride of an anti-freezingagent, etc. Although SUS440C is high in hardness, it is at a low levelin corrosion resistance among stainless steels. As a result, use ofrolling bearings made of SUS440C in an exposed-to-water environment isassociated with a problem that they are prone to rust.

Patent document 1 discloses a martensite-type stainless steel that ishigh in hardness and corrosion resistance and hence can be used suitablyto form a bearing. In Patent document 1, the hardness is increased bysetting the content of N higher than in conventional martensite-typestainless steels and optimizing the total content of C and N and thecontent ratio C/N. On the other hand, the corrosion resistance isincreased by adding a corrosion resistance increasing element such as Moand adding a proper amount of N in the matrix in the form of a solidsolution.

BACKGROUND ART DOCUMENT Patent Document

Patent document 1: Japanese Patent No. 4,952,888

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

Exhibiting high hardness and corrosion resistance, the martensite-typestainless steel disclosed in Patent document 1 is certainly suitable forformation of a bearing. However, in manufacturing, for example, theouter ring of a rolling bearing using this stainless steel, it is turnedon a lathe into a ring having predetermined dimensions and thensubjected to heat treatment to secure certain hardness. Usually, thisheat treatment is performed in air (oxygen-containing atmosphere). Thus,oxygen in the air reacts with iron in the surface of the stainlesssteel, whereby an iron-oxide-based coating (what is called scale) isformed. The scale is a coating that is not necessary in a product andhence scale removal processing is necessary, which is cumbersome.

Furthermore, in the heat treatment in air, the contents of the componentvary as exemplified by increase of the content of N (nitrogenabsorption) and decrease of the content of C (decarburization) in, forexample, a region to a depth of 0.7 mm from the surface of the stainlesssteel. In removing scale, removal processing (referred to as “processingfor removal of scale etc.” which includes scale removal processing andprocessing for removal of portions where the content variations haveoccurred) needs to be performed taking into consideration removal ofportions where content variations such as nitrogen absorption anddecarburization have occurred. Thus, in the processing for removal ofscale etc., a portion to the depth of about 1 mm from the surface needsto be removed to prevent scale, a nitrogen absorption region, and adecarburization region from remaining. As such, the processing forremoval of scale etc. causes a large material loss.

One method for preventing formation of scale, a nitrogen absorptionregion, and a decarburization region by heat treatment would be toperform heat treatment in, for example, a vacuum atmosphere(oxygen-absent atmosphere). If heat treatment is performed in a vacuumatmosphere, none of scale, a nitrogen absorption region, and adecarburization region are formed and hence no processing for removal ofscale etc. is necessary. However, a problem arises that heat treatmentin a vacuum atmosphere causes formation of rust on the surface (i.e.,the corrosion resistance lowers) even if a stainless steel that exhibitshigh corrosion resistance is used. As for this problem, in Patentdocument 1, no attention is paid to omission of the processing forremoval of scale etc. and no countermeasure against lowering ofcorrosion resistance due to this is taken.

The present inventors have studied diligently to investigate the causeof the above problems and have found first that shortage of Cr in a verythin, nano-level surface layer part having a depth of several tens ofnanometers from the surface renders formation of an effectivepassivation film difficult.

The present invention has been made to solve the above problems, and anobject of the present invention is therefore to provide arolling-sliding member that is high in hardness and continues to have apassivation film reliably even after being subjected to a process thatdoes not require any processing for removal of scale etc., as well as arolling bearing using the same and a method for manufacturing therolling-sliding member.

Means for Solving the Problems

Firstly, the present invention provides a rolling-sliding memberincluding: 0.15 mass % or larger and smaller than 0.70 mass % of C; 0.05to 1.00 mass % of Si; 0.05 to 1.00 mass % of Mn; 0.03 mass % or smallerof P; 0.03 mass % or smaller of S; 0.001 to 0.500 mass % of Cu; 0.05 to0.50 mass % of Ni; 11.0 to 18.0 mass % of Cr; 0.05 to 2.00 mass % of Mo;0.01 to 0.50 mass % of W; 0.01 to 0.50 mass % of V; 0.05 to 0.40 mass %of N; 0.02 mass % or smaller of O; 0.080 mass % or smaller of Al; 0.0005to 0.0050 mass % of B; provided that the total content of C and N islarger than 0.4 mass % and smaller than 0.7 mass %, and a content ratioC/N is 0.75 or larger; and the remainder being Fe and unavoidableimpurities, in which no Cr-deficient layer exists in a surface layerpart having a depth of at least 40 nm from a surface of therolling-sliding member.

The fundamental composition of this rolling-sliding member is the sameas that disclosed in Patent document 1. With the additional feature thatno Cr-deficient layer exists in a surface layer part, therolling-sliding member has a passivation film reliably even if it ismanufactured by a process that does not require any processing forremoval of scale etc. As a result, high hardness and corrosionresistance can be secured.

The rolling-sliding member according to the present invention means ametal member having a contact surface that comes into relative rollingcontact or sliding contact with a counterpart member. Specific examplesof the rolling-sliding member are constituent members of a rollingbearing, a linear bearing, and a ball screw. The linear bearing is abearing in which a first raceway member and a second raceway member thathave respective straight raceway surfaces and are opposed to each othermake straight movement relative to each other with rolling of aplurality of rolling bodies disposed between the first raceway memberand the second raceway member. Examples of the rolling bodies used inthe linear bearing are balls and rollers. Another type of the linearbearing is a recirculating linear bearing in which rolling bodiescirculate. The ball screw is a bearing in which each of confrontingsurfaces of a screw shaft and a nut is formed with a screw groove inwhich balls (a plurality of rolling bodies) are disposed rollably.

The rolling bearing includes an outer ring, an inner ring, a pluralityof rolling bodies disposed rollably between the outer ring and the innerring, and a holding device which holds the plurality of rolling bodiesso that the plurality of rolling bodies are arranged at predeterminedintervals in the circumferential direction. It is most preferable to usethe rolling-sliding member according to the present invention as theouter ring of a rolling bearing among the above-mentioned variousrolling-sliding members. This is because although the inner ring, therolling bodies, and the holding device are also rolling-sliding members,the outer ring is the outermost component of the rolling bearing andhence is most prone to rust when put in an exposed-to-water environmentand exposed to water, a salt content, or the like.

Additionally, the present invention also provides a method formanufacturing a rolling-sliding member, the method including: performingvacuum heat treatment, to attain hardness of 55 HRC or higher, on amartensite steel member including: 0.15 mass % or larger and smallerthan 0.70 mass % of C; 0.05 to 1.00 mass % of Si; 0.05 to 1.00 mass % ofMn; 0.03 mass % or smaller of P; 0.03 mass % or smaller of S; 0.001 to0.500 mass % of Cu; 0.05 to 0.50 mass % of Ni; 11.0 to 18.0 mass % ofCr; 0.05 to 2.00 mass % of Mo; 0.01 to 0.50 mass % of W; 0.01 to 0.50mass % of V; 0.05 to 0.40 mass % of N; 0.02 mass % or smaller of O;0.080 mass % or smaller of Al; 0.0005 to 0.0050 mass % of B; providedthat the total content of C and N is larger than 0.4 mass % and smallerthan 0.7 mass %, and a content ratio C/N is 0.75 or larger; and theremainder being Fe and unavoidable impurities; and thereafter performingprocessing of removing a surface layer part of the martensite steelmember.

In the above manufacturing method, a region of performing the processingof removing the surface layer part may be a region having a depth of atleast 40 nm from a surface of the martensite steel member. This isbecause a Cr-deficient layer tends to be formed in a region having adepth of 40 nm from the surface in the case where vacuum heat treatmentis performed to dispense with the processing for removal of scale etc.Thus, reduction of corrosion resistance can be prevented effectively byremoving the region having a depth of at least 40 nm from the surface.

In the case where this rolling-sliding member is used as the outer ringof a rolling bearing, it suffices that the processing of removing asurface layer part be performed on at least the outer circumferentialsurface and the side surfaces of the outer ring. That is, the processingof removing a surface layer part need not always be performed on theinner surface of the outer ring. This is because, in the case where theraceways of the rolling bearing are sealed by sealing members, water isnot prone to intrude to reach the raceways, and hence formation of rustis hardly caused on the inner surface, formed with the raceway, of theouter ring.

In the present invention, an expression “AA to BB” indicating anumerical range means “larger (or higher) than or equal to AA andsmaller (or lower) than or equal to BB” unless otherwise specified.

Advantage of the Invention

Being the same in fundamental composition as the rolling-sliding memberdisclosed in Patent document 1, the rolling-sliding member according tothe present invention exhibits high hardness and corrosion resistanceintrinsically. With the additional feature that no Cr-deficient layerexists in a surface layer part, the rolling-sliding member has apassivation film reliably. Thus, even if it is manufactured by a processthat does not require any processing for removal of scale etc., it doesnot have an iron-based coating as formed due to presence of aCr-deficient layer. High corrosion resistance can therefore be secured.Thus, rust can be prevented effectively even if the rolling-slidingmember is used as the outer ring of a rolling bearing that is used in anexposed-to-water environment. As a result, the rolling-sliding membercan be used in seaside areas where the salt concentration in the air ishigh and conventional rolling-sliding members are difficult to use.

In the method for manufacturing a rolling-sliding member according tothe present invention, none of scale, nitrogen absorption region, anddecarburization region are formed because the heat treatment isperformed in a vacuum atmosphere (oxygen-absent atmosphere). Thus, it isnot necessary to perform, after the heat treatment, any processing forremoval of scale etc., which is indispensable conventionally. With theadditional feature that the processing of removing a surface layer partis performed, a Cr-deficient layer that is formed by the vacuum heattreatment can be removed. Since it suffices that the processing ofremoving a surface layer part be performed in nm order, the amount ofremoved material is extremely smaller than in the processing for removalof scale etc. in which a surface layer part is removed in mm order. Thisprocessing of removing a surface layer part is therefore advantageousalso in terms of material cost. Furthermore, since the cycle time ofremoval processing is proportional to the amount of removed material,the shortening of the cycle time can increase the yield per unit time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cutaway perspective view showing the structure ofa common rolling bearing.

FIG. 2 is a sectional view of a rolling bearing that has a sealingmember for sealing drive surfaces.

FIG. 3 is a graph showing to what extent Cr exists in a surface layerpart.

MODE FOR CARRYING OUT THE INVENTION

First, a description will be made of a fundamental composition of amartensite steel material that is a base of a rolling-sliding member.This rolling-sliding member is the same in fundamental composition asthe rolling-sliding member disclosed in Patent document 1, and hasDSR-40N as a product on the market. More specifically, the fundamentalcomposition includes 0.15 mass % or larger and smaller than 0.70 mass %of C; 0.05 to 1.00 mass % of Si; 0.05 to 1.00 mass % of Mn; 0.03 mass %or smaller of P; 0.03 mass % or smaller of S; 0.001 to 0.500 mass % ofCu; 0.05 to 0.50 mass % of Ni; 11.0 to 18.0 mass % of Cr; 0.05 to 2.00mass % of Mo; 0.01 to 0.50 mass % of W; 0.01 to 0.50 mass % of V; 0.05to 0.40 mass % of N; 0.02 mass % or smaller of O; 0.080 mass % orsmaller of Al; 0.0005 to 0.0050 mass % of B; provided that the totalcontent of C and N is larger than 0.4 mass % and smaller than 0.7 mass%, and a content ratio C/N is 0.75 or larger; and the remainder being Feand unavoidable impurities.

Carbon (C) serves to secure necessary strength and corrosion resistance,and forms carbides by combining with carbide forming elements such asCr, Mo, W, V, and Nb. Carbon also serves to secure necessary hardness byforming a solid solution in the matrix at the time of quenching, therebycausing the matrix to have a martensite structure.

Being an interstitial element, N increases both of corrosion resistanceand hardness. The corrosion resistance is increased when N is added tothe matrix in the form of a solid solution. The elements Ni, Cr, and Vincrease the amount of dissolved nitrogen.

Chromium (Cr), which is the main component of a surface layerpassivation film, increases the corrosion resistance. Copper (Cu) alsoincreases the corrosion resistance, and is particularly effective atsuppressing erosion of hydrochloric acid. Molybdenum (Mo) also increasesthe corrosion resistance.

Silicon (Si) is added mainly as a deoxidizer or for addition ofnitrogen. Manganese (Mn) increases the quenching performance, and has aneffect of preventing reduction in toughness by fixing S that iscontained unavoidably. Tungsten (W) increases the quenching performance.Aluminum (Al) is added as a deoxidizer. Boron (B) strengthens grainboundaries and thereby lowers the probability of occurrence of brakingat the time of quenching or sub-zero treatment. Phosphorus (P), S, and Oare contained in steel unavoidably.

The rolling-sliding member may contain the following elements in thefollowing content ranges in addition to the above essential elements:

0.001 mass %≤Co≤0.500 mass %

0.001 mass %≤Se≤0.300 mass %

0.001 mass %≤Te≤0.300 mass %

0.0002 mass %≤Ca≤0.1000 mass %

0.001 mass %≤Pb≤0.200 mass %

0.001 mass %≤Nb≤0.300 mass %

0.001 mass %≤Ta≤0.300 mass %

Ti≤0.200 mass %

0.001 mass %≤Zr≤0.300 mass %.

In the case of manufacturing a rolling-sliding member using the abovemartensite steel material, the material is formed into a predeterminedshape by casting or forging and then subjected to heat treatment such asquenching, sub-zero treatment, and tempering to obtain certain hardnessand for other purposes. In the case where high dimensional accuracy isrequired, it is preferable to cut a member formed by casting or forgingso as to have a rough shape, into predetermined dimensions.

The quenching treatment is performed by heating a steel material to aquenching temperature or a solution treatment temperature of 1,020° C.to 1,150° C. and then cooling it quickly at a predetermined cooling rateby oil quenching, gas cooling, or the like. In the sub-zero treatment,the steel material is again cooled quickly using a freezing mixture orrefrigerant of 0° C. or lower soon after the quenching. For example, dryice, dry ice plus alcohol (−80° C.), carbon dioxide gas (−130° C.), orliquid nitrogen (−196° C.) can be used as the freezing mixture orrefrigerant. In the tempering treatment, the steel material as subjectedto the sub-zero treatment is heated to 150° C. to 450° C. As a result ofthe above heat treatment, the steel material is given Rockwell hardnessthat is at least larger than or equal to 55 HRC, which is equivalent tothe value of SUS440C.

The heat treatment described above is performed in a vacuum atmosphere.It is also preferable to perform the heat treatment in an inert gasatmosphere by introducing a nitrogen gas or the like, rather than in avacuum atmosphere. Since the above heat treatment is performed in anoxygen-absent atmosphere, no scale, nitrogen absorption region, ordecarburization region is formed in the surface of the rolling-slidingmember and hence it is not necessary to perform any processing forremoval of scale etc. after the heat treatment.

However, we found that a Cr-deficient layer where the content of Cr isclearly small is formed within a region of a depth (thickness) of about40 nm from the surface. Thus, if the steel material is used withoutbeing subjected to any processing after the heat treatment, no effectivepassivation film is formed due to the shortage of Cr and an iron oxidecoating is formed instead as a result of a phenomenon that iron in thesteel material combines with oxygen in the air, resulting in largereduction in corrosion resistance. The term “Cr-deficient layer” as usedherein means a layer where the content of Cr is clearly smaller than anintrinsic range 11.0 to 18.0 mass % of the rolling-sliding member.

In view of the above, it is necessary to remove a very thin surfacelayer part after the heat treatment. The thickness (depth) of a layer tobe removed is at least larger than or equal to 40 nm, preferably largerthan or equal to 100 nm, from the surface. A clear Cr-deficient layercan be removed properly if a layer whose thickness is larger than orequal to 40 nm from the surface is removed. A Cr-deficient layer can beremoved fully if a layer whose thickness is larger than or equal to 100nm from the surface is removed. On the other hand, although there are noparticular limitations on the upper limit of the thickness of a layer tobe removed, it is preferable that the upper limit be at least smallerthan a thickness (0.7 mm) of the conventional processing for removal ofscale etc. This is because it is desirable to reduce the amount ofremoved material to a minimum necessary level if the material cost andthe productivity (shortening of the processing time) are taken intoconsideration. Thus, it is much preferable that the thickness of a layerto be removed be smaller than or equal to 100 μm from the surface and itis far preferable that it be smaller than or equal to 150 nm from thesurface. There are no particular limitations on the processing methodfor removing a surface layer part; any method capable of removing asurface layer part can be employed, such as polishing, barrel polishing,cutting, and chemical processing.

A rolling-sliding member produced in the above-described manner is highin corrosion resistance because an effective passivation film is formedreliably in the surface thereof. In terms of pitting potential, thisrolling-sliding member is equivalent to SUS630 which is said to be highin corrosion resistance. As such, this rolling-sliding member issuitable as a member for use in an exposed-to-water environment, and canbe used as a rolling bearing used for, for example, a slide door that isinstalled in an automobile, an industrial machine, a warehouse, or thelike so as to be exposed directly to an external environment (ambientatmosphere). This rolling-sliding member is particularly suitable foruse as the outer ring of a rolling bearing among such uses.

As shown in FIG. 1, a common rolling bearing 1 of this type includes anouter ring 2, an inner ring 3, a plurality of rolling bodies 4 which aredisposed rollably between the outer ring 2 and the inner ring 3, and aholding device 5 for holding the rolling bodies 4 so that the rollingbodies 4 are arranged at predetermined intervals in the circumferentialdirection. Since in this manner the outer ring 2 is the outermostcomponent of the rolling bearing 1, it is most prone to rust when therolling bearing 1 is used in an exposed-to-water environment. If theouter ring 2 rusts, resulting rust powder sticks to a slide rail andpossibly impair its appearance. It is therefore preferable to use therolling-sliding member according to the present invention as the outerring 2.

In this case, basically, it is necessary to perform processing ofremoving a Cr-deficient layer on all of the outer circumferentialsurface, the side surfaces, and the inner circumferential surface (thesurface opposed to the inner ring 3) of the outer ring 2. However, amongrolling bearings are ones in which, as in a rolling bearing 10 for aslide door shown in FIG. 2, the space between an outer ring 12 and aninner ring 13 is sealed by sealing members 16. In the rolling bearing 10having such a structure, it may suffice to perform processing ofremoving a Cr-deficient layer on only the outer circumferential surfaceand the side surfaces of the outer ring 2. In FIG. 2, symbol 14 denotesa rolling body and symbol 15 denotes a holding device for holding therolling bodies 14 at predetermined intervals in the circumferentialdirection.

In this rolling bearing 10 for a slide door, in many cases, the innercircumferential surface, including the raceway surface, of the outerring 12 is not subjected to finishing such as polishing after beingsubjected to cutting and vacuum heat treatment as in the conventionalcase. More specifically, in the common rolling bearing 1, it is foundfrequently that finishing is performed on only the raceway surface(inner circumferential surface) which is a curved surface but is notperformed on the side surfaces and the outer circumferential surface. Onthe other hand, in the present invention, finishing is performed on onlythe side surfaces or the outer circumferential surface but not performedon the raceway surface; the present invention is right opposite to theconventional case in this respect. Thus, in such a rolling bearing 10for a slide door, the time and labor and the cost of processing can bereduced.

In the case where rolling bearings are used in an exposed-to-waterenvironment, the inner ring may also rust. It is therefore preferable touse a rolling-sliding member according to the present invention also asthe inner ring. As in the case of the outer ring, basically, it ispreferable to perform processing of removing a Cr-deficient layer on allof the outer circumferential surface (the surface opposed to the outerring), the side surfaces, and the inner circumferential surface.However, in the case shown in FIG. 2 in which the space between theouter ring and the inner ring is sealed by the sealing members, theprocessing of removing a Cr-deficient layer may be performed on only theinner circumferential surface and the side surfaces.

The rolling bodies and the holding device may be made of the samematerials as those of known, common rolling bearings. For example, therolling bodies may be made of a carbon steel or SUJ2. For example, theholding device may be made of a resin-based material such as reinforcedpolyamide.

Examples

Hardness (Rockwell hardness) of the outer rings of rolling bearings thatwere treated under various sets of heat treatment conditions shown inTable 1 was measured and evaluated. Results are also shown in Table 1.As for the dimensions of the outer ring, the outer diameter was 24 mm,the inner diameter was 18 mm, and the width was 8 mm. DSR-40N was usedas a martensite steel material. The outer ring was produced by cutting arod material without subjecting a resulting material to processing ofremoving a surface layer such as polishing. Heat treatment was performedusing a vacuum furnace. Quick cooling that was performed after quenchingwas carried out by introducing a nitrogen gas into the furnace.

TABLE 1 Manufacture Manufacture Manufacture Manufacture ManufactureManufacture Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Quenching Temperature (° C.) 1,062 1,038 1,050 1,050 1,050 1,050 Time(min) 70 50 60 60 60 60 Sub-zero treatment Temperature (° C.) −60 −60−72 −48 −60 −60 Time (min) 30 30 40 20 30 30 Tempering Temperature (°C.) 180 180 180 180 192 168 Time (min) 120 120 120 120 130 110 Hardness(HRC) 58.2 57.3 57.9 57.3 57.1 58.4

It was confirmed from the results of Table 1 that the Rockwell hardnesscan be made larger than or equal to 55 HRC by performing vacuum heattreatment on DSR-40N under the above sets of heat treatment conditions.

Subsequently, influence of execution/non-execution of the surface layerpart removal processing on the corrosion resistance was measured andevaluated using the outer ring of Manufacture Example 1. The outer ringof Manufacture Example 1 whose outer circumferential surface wassubjected to the surface layer part removal processing by polishing awaya surface layer part having a depth of 100 μm from the surface wasemployed as Working Example. On the other hand, the outer ring ofManufacture Example 1 itself that was not subjected to the surface layerpart removal processing was employed as Comparative Example. As forcorrosion resistance, pitting potential was measured according to JIS G0577: 2014. The contents of JIS G 0577: 2014 are incorporated herein byreference.

A measured pitting potential of Working Example (with surface layer partremoval) was 116 mV, which is equivalent to the value of SUS630 which isgenerally said to be high in corrosion resistance. In contrast, ameasured pitting potential of Comparative Example was −12 mV. Thus,whereas in Comparative Example (without surface layer part removal)proper corrosion resistance cannot be obtained though it is high inhardness, it was confirmed that in Example (with surface layer partremoval) both of high hardness and high corrosion resistance aresecured.

Subsequently, why execution/non-execution of the surface layer partremoval causes a difference in corrosion resistance was investigated. Inthe investigation, an element composition profile in the depth directionwas analyzed using an Auger electron spectroscopic analyzer byrepeating, starting from the outermost surface layer part, an elementcomposition analysis and nm-order removal of a material layer by ionsputtering. The depth was obtained by converting the ion sputteringtime. Results are shown in FIG. 3.

It is seen from the results shown in FIG. 3 that in Comparative Example(without surface layer part removal), the Cr ratio clearly is smaller ina region having a depth of about 40 nm from the surface (i.e.,Cr-deficient region) than a reference (constant) Cr ratio in a regionwhere the depth is around 100 nm. Thus, it was found that the reason ofthe corrosion resistance reduction is that no effective passivation filmis formed adjacent to the surface. It is seen from the above measurementresult that it suffices that the thickness (depth) of a layer to beremoved be at least larger than or equal to 40 nm from the surface inthe surface layer part removal processing. That is, it is expected thata state that the Cr ratio is constant from the surface part, that is, noCr-deficient layer exists, would be established by removing a surfacelayer part having a depth of 40 nm or more from the surface.

In contrast, in Working Example (with surface layer part removal), it isseen that no Cr-deficient layer exists within a region having a depth of10 nm or more from the surface. Furthermore, a sufficiently large Crratio was detected even at a depth of 2 nm, which means that noCr-deficient layer exists even substantially at the surface. That is, itcan be said that the Cr ratio is kept almost constant as the positiongoes deeper from the surface. It has thus been found that in WorkingExample almost no Cr-deficient layer occurs and high corrosionresistance can be secured because Cr exists adjacent to the surface.

The present application is based on Japanese Patent Application No.2016-030498 filed on Feb. 19, 2016, the contents of which areincorporated herein by reference.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

-   -   1, 10: Rolling bearing    -   2, 12: Outer ring    -   3, 13: Inner ring    -   4, 14: Rolling body    -   5, 15: Holding device    -   16: Sealing member

1. A method for manufacturing a rolling-sliding member, the methodcomprising: performing vacuum heat treatment, to attain hardness of 55HRC or higher, on a martensite steel member comprising: 0.15 mass % orlarger and smaller than 0.70 mass % of C; 0.05 to 1.00 mass % of Si;0.05 to 1.00 mass % of Mn; 0.03 mass % or smaller of P; 0.03 mass % orsmaller of S; 0.001 to 0.500 mass % of Cu; 0.05 to 0.50 mass % of Ni;11.0 to 18.0 mass % of Cr; 0.05 to 2.00 mass % of Mo; 0.01 to 0.50 mass% of W; 0.01 to 0.50 mass % of V; 0.05 to 0.40 mass % of N; 0.02 mass %or smaller of O; 0.080 mass % or smaller of Al; 0.0005 to 0.0050 mass %of B; provided that the total content of C and N is larger than 0.4 mass% and smaller than 0.7 mass %, and a content ratio C/N is 0.75 orlarger; and the remainder being Fe and unavoidable impurities; andthereafter performing processing of removing a surface layer part of themartensite steel member.
 2. The method for manufacturing arolling-sliding member according to claim 1, wherein a region ofperforming the processing of removing the surface layer part is a regionhaving a depth of at least 40 nm from a surface of the martensite steelmember.
 3. The method for manufacturing a rolling-sliding memberaccording to claim 1, wherein the rolling-sliding member is an outerring of a rolling bearing; and the processing of removing the surfacelayer part is performed on at least an outer circumferential surface andside surfaces of the outer ring.
 4. The method for manufacturing arolling-sliding member according to claim 2, wherein the rolling-slidingmember is an outer ring of a rolling bearing; and the processing ofremoving the surface layer part is performed on at least an outercircumferential surface and side surfaces of the outer ring.